PATCH: math error messages

[Peter Stephenson <p.stephenson@xxxxxxxxxxx>]

On Mon, 28 Oct 2013 17:55:05 +0000
Peter Stephenson <p.stephenson@xxxxxxxxxxx> wrote:
> >     zsh: bad math expression: operand expected at `'
>
> The error you got comes from it being empty, so there's no
> number, which is what it's complaining about, slightly cryptically.

Is anyone particularly attached to the current error messages?  I think
the following are a bit clearer for the two specific cases, although I'm
not sure about the word "string".  I used it in order to keep the
standard math error prefix and avoid repeating "expression".  I could
say "argument" but that means a lot of possible things, most commonly a
command line argument which would be inaccurate.

% print $foo[]
zsh: bad math expression: empty string
% print $foo[3+]
zsh: bad math expression: operand expected at end of string

I have not changed any behaviour, only messages.  I've noted that while
$(()) returns 0, $foo[$unset] is an error.  I'm happy with the latter
and I think the former was forced on us by standards.

diff --git a/Src/math.c b/Src/math.c
index eae283d..b21a3ad 100644
--- a/Src/math.c
+++ b/Src/math.c
@@ -1374,6 +1374,19 @@ mathevalarg(char *s, char **ss)
     mnumber x;
     int xmtok = mtok;
 
+    /*
+     * At this entry point we don't allow an empty expression,
+     * whereas we do with matheval().  I'm not sure if this
+     * difference is deliberate, but it does mean that e.g.
+     * $array[$ind] where ind hasn't been set produces an error,
+     * which is probably safe.
+     *
+     * To avoid a more opaque error further in, bail out here.
+     */
+    if (!*s) {
+	zerr("bad math expression: empty string");
+	return (zlong)0;
+    }
     x = mathevall(s, MPREC_ARG, ss);
     if (mtok == COMMA)
 	(*ss)--;
@@ -1401,6 +1414,7 @@ checkunary(int mtokc, char *mptr)
     }
     if (errmsg) {
 	int len, over = 0;
+	char *errtype = errmsg == 2 ? "operator" : "operand";
 	while (inblank(*mptr))
 	    mptr++;
 	len = ztrlen(mptr);
@@ -1408,9 +1422,12 @@ checkunary(int mtokc, char *mptr)
 	    len = 10;
 	    over = 1;
 	}
-	zerr("bad math expression: %s expected at `%l%s'",
-	     errmsg == 2 ? "operator" : "operand",
-	     mptr, len, over ? "..." : "");
+	if (!*mptr)
+	    zerr("bad math expression: %s expected at end of string",
+		errtype);
+	else
+	    zerr("bad math expression: %s expected at `%l%s'",
+		 errtype, mptr, len, over ? "..." : "");
     }
     unary = !(tp & OP_OPF);
 }
diff --git a/Test/C01arith.ztst b/Test/C01arith.ztst
index 71c8a19..c19135c 100644
--- a/Test/C01arith.ztst
+++ b/Test/C01arith.ztst
@@ -134,11 +134,11 @@
 
   print $(( a = ))
 1:empty assignment
-?(eval):1: bad math expression: operand expected at `'
+?(eval):1: bad math expression: operand expected at end of string
 
   print $(( 3, ))
 1:empty right hand of comma
-?(eval):1: bad math expression: operand expected at `'
+?(eval):1: bad math expression: operand expected at end of string
 
   print $(( 3,,4 ))
 1:empty middle of comma

pws